The quantitative determination of analytes in body fluids is of great importance in the diagnoses and maintenance of certain physiological abnormalities. For example, lactate, cholesterol and bilirubin should be monitored in certain individuals. In particular, it is important that diabetic individuals frequently monitor the glucose level in their body fluids in order to manage its level. The results of such tests can be used to determine what, if any, insulin or other medication needs to be administered. In one type of blood-glucose testing system, sensors are used to test a sample of blood.
A test sensor contains biosensing or reagent material that reacts with blood glucose. In some mechanisms, the testing end of the sensor is adapted to be placed into the fluid being tested, for example, blood that has accumulated on a person's finger after the finger has been lanced. The fluid is drawn into a capillary channel that extends in the sensor from the testing end to the reagent material by capillary action so that a sufficient amount of fluid to be tested is drawn into the sensor. The fluid then chemically reacts with the reagent material in the sensor resulting in an electrical signal indicative of the glucose level in the fluid being tested. This signal is supplied to the meter via contact areas located near the rear or contact end of the sensor and becomes the measured output. In other mechanisms, the sensor has a reagent area upon which the blood is applied. The resulting chemical reaction produces a color change. When the sensor is inserted into an instrument, the color change can be optically measured and converted into an equivalent glucose concentration value.
Diagnostic systems, such as blood-glucose testing systems, typically calculate the actual glucose value based on a measured output and the known reactivity of the reagent-sensing element (test sensor) used to perform the test. The reactivity or lot-calibration information of the test sensor may be given to the user in several forms including a number or character that they enter into the instrument. Another method for calibrating strips contained within a package is to include a calibration chip within the sensor packaging that is inserted into the test instrument. When plugged into the instrument, the calibration chip's memory element is electrically coupled to the instrument's microprocessor board for directly reading the stored calibration information by the instrument.
These methods suffer from the disadvantage of relying on the user to properly enter the calibration information, which some users may not enter at all or may input incorrectly. In this event, the test sensor may use the wrong calibration information and thus return an erroneous result. Where a calibration chip is contained within the sensor packaging, the calibration chip can be easily lost or misplaced, resulting in an inability to enter the sensor information via the calibration chip.
Improved systems use an auto-calibration label that is affixed to a sensor cartridge. The auto-calibration label is read automatically when the cartridge is loaded into the meter and requires no additional user intervention. However, such an auto-calibration method requires a cartridge that can be loaded into the meter, that can provide environmental protection for long-term stability of the stored sensors, and that it can provide automated access to the sensors. Simpler forms of such a cartridge, where sensors are sealed in individual compartments, generally provide little or no flexibility to vary the number of sensors that can packaged and the maximum is limited by the maximum acceptable cartridge size. Cartridges with sensors stacked within a common compartment can support larger and potentially variable numbers of stored sensors, but providing a good environmental seal after the first sensor is extracted is difficult, has associated technical complexity and costs associated with automated sensor access, and, in simpler forms, may be inflexible in the number of sensors that can be packaged.
It would be desirable to provide a device and method that provides the lot calibration information of the test sensor to instruments or meters in a reliable manner without the complexity, cost, and constraints of an automated cartridge, without the need for manual entry of calibration information by the user, and without the need for a separate calibration chip that can be lost. This is particularly desirable for systems designed to work with individual sensors packaged in a bottle or other container that is separate from the instrument and flexible in the number of sensors that can be packaged rather than in a specialized cartridge that is loaded into the instrument for automatic sensor dispensing.